Dynamic power line access connection

ABSTRACT

A method of connecting a power line modem to an external network. The method includes receiving, by the power line modem, a plurality of packets directly transmitted from a plurality of neighboring devices connected to the powerlines, determining for each of the plurality of neighboring devices, a cost of a route to an access unit, through the neighboring device, responsive to the received packets, and selecting an access unit to service the power line modem, responsive to the determination of the costs.

RELATED APPLICATIONS

This application claims the benefit under § 119(e) of U.S. provisionalpatent application 60/307,251, filed Jul. 23, 2001, the disclosure ofwhich document is incorporated herein by reference. The presentapplication is also a continuation-in-part (CIP) of PCT applicationPCT/IL01/00745, published as WO 02/15413, filed Aug. 12, 2001, thedisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to signal transmission over power lines.

BACKGROUND OF THE INVENTION

Electric power lines can be used to access external (backbone)communication networks, such as the Internet. For example, EP patentpublication 0 975 097, the disclosure of which is incorporated herein byreference, describes a method of exchanging data between a customer anda service provider over low and medium voltage AC electric powernetworks.

In forming electrical access power connections, similar to asynchronousdigital subscriber line (ADSL) connections, each user is provided with ahome electrical power modem for connection to the power lines within theuser's home or office. In addition, a service provider locates an accessmodem on the electric power lines at a connection point to the externalnetwork, near the user's home. Some service providers connect more thanone home electrical power modem to a single access modem in order toreduce the number of access modems required. The maximal distancebetween the home modems and the access modem is, however, limited, dueto the relatively high level of noise on electrical power lines.

SUMMARY OF THE INVENTION

An aspect of some embodiments of the present invention relates to auser-end power-line modem which dynamically chooses the access niodemfrom which to receive access service. Optionally, the user-end modem isnot configured with a specific group of access modems from which toreceive service, but rather selects the access modem based on a query ofneighboring devices.

In some embodiments of the invention, the user-end modem chooses betweenone or more access modems within a communication distance from theuser-end modem and one or more access modems beyond a distance allowingdirect communication (i.e., without passing through one or more otherdevices serving as repeaters), but connectable through one or morerepeaters. The repeaters optionally transmit messages they receive ontothe same power lines from which the messages were received. Therepeaters may be dedicated devices used only for repeating and/or may beother end-user modems and/or access modems. In these embodiments, aservice provider does not need to locate a plurality of access modemswithin a communication distance from each user-end modem, in order toprovide service or service redundancy.

In some embodiments of the invention, the access modems belong to aplurality of different service providers and/or connect to a pluralityof different types of backbone networks. Alternatively or additionally,at least some of the access modems belong to the same service providersand/or connect to the same backbone network.

The user-end modem optionally transmits route query packets on the powerline, in order to determine the available routes to access modems and acost associated with each route. Neighboring devices optionally respondto the query packets with routing information they have on theconnection to one or more access units. The querying user-end modemoptionally selects an access unit from which to receive serviceaccording to the responses.

In some embodiments of the invention, the query packets are transmittedin a plurality of power levels, which levels affect the number ofneighboring devices on the one hand and the extent of the power linesegment which cannot be used concurrently with querying user-end modem.

The cost associated with each route optionally is a function of thenumber of intermediate devices between the user modem and the accessunit and/or the data rate along the route between the user modem and theaccess unit. Alternatively or additionally, the cost of a route dependson the transmission power level required to communicate between thedevices along the route.

There is therefore provided in accordance with an embodiment of thepresent invention, a method of connecting a power line modem to anexternal network, comprising receiving, by the power line modem, aplurality of packets directly transmitted from a plurality ofneighboring devices connected to the power lines, determining for eachof the plurality of neighboring devices, a cost of a route to an accessunit, through the neighboring device, responsive to the receivedpackets, and selecting an access unit to service the power line modem,responsive to the determination of the costs.

Optionally, at least one of the neighboring devices comprises an accessunit. Alternatively, at least one of the neighboring devices is not anaccess unit. Optionally, at least one of the neighboring devicescomprises a second user modem. Optionally, determining for the pluralityof neighboring devices the cost of a route to an access unit comprisesdetermining for a plurality of the neighboring devices the cost ofroutes to a single access unit. Optionally, determining for theplurality of neighboring devices the cost of a route to an access unitcomprises determining for a plurality of the neighboring devices thecost of routes to a plurality of different access units.

Optionally, selecting the access unit comprises selecting responsive tothe determined cost and responsive to one or more parameters of thedifferent access units. Optionally, selecting the access unit comprisesselecting responsive to the determined cost and responsive to the loadon the different access units. Alternatively or additionally, selectingthe access unit comprises selecting responsive to the determined costand responsive to the external networks to which the different accessunits lead.

Optionally, the received plurality of packets are generated by theneighboring devices, periodically, without receiving prompting messagesfrom the power line modem.

Alternatively or additionally, the method includes transmitting one ormore network discovery packets on the power line and wherein thereceived plurality of packets are generated responsive to at least oneof the one or more discovery packets. Optionally, transmitting the oneor more network discovery packets comprises transmitting a plurality ofpackets with different transmission power levels. Optionally, the methodincludes determining for each of the power levels a number of devicesresponding to the transmitted packet with that power level.

Optionally, transmitting the one or more network discovery packetscomprises transmitting with increasing power levels until a route with acost beneath a predetermined threshold is found. Optionally, determiningthe cost comprises determining the cost responsive to a number ofintermediate devices along the route to the access unit. Optionally,determining the cost comprises determining the cost responsive to a datarate of one or more hops of the route to the access unit.

Optionally, determining the cost comprises determining the costresponsive to a power level required to communicate with the neighboringdevice. Optionally, determiiing the cost comprises determining the costresponsive to a number of neighboring devices of the modem at therequired power level. Optionally, determining the cost comprisesdetermining a neighbor segment cost of a network segment between thepower line modem and a neighboring device and adding the neighborsegment cost to an access cost of a segment from the neighboring deviceto an access unit, which access cost is received from the neighboringdevice. Optionally, the selected access unit is not within atransmission range of the power line modem.

There is further provided in accordance with an embodiment of thepresent invention, a power line modem, comprising a power line interfacefor receiving packets from the power line and a controller adapted toreceive a plurality of packets directly transmitted from a plurality ofneighboring devices connected to the power lines; to determine, for theplurality of neighboring devices, a cost of a route to an access unit,through the neighboring device, responsive to the received packets; andto select an access unit from which to receive service, responsive tothe determination of the costs.

BRIEF DESCRIPTION OF FIGURES

Particular exemplary embodiments of the invention will be described withreference to the following description, in conjunction with the figures,wherein identical structures, elements or parts which appear in morethan one figure are preferably labeled with a same or similar number inall the figures in which they appear, in which:

FIG. 1 is a schematic block diagram of a transmission system utilizingelectric power lines, in accordance with an embodiment of the presentinvention;

FIG. 2 is a schematic illustration of a data packet transmitted on apower line, in accordance with an embodiment of the present invention;and

FIG. 3 is a flowchart of acts performed in provisioning and selecting anaccess unit, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic block diagram of a transmission system 100utilizing an electric power line 112, in accordance with an embodimentof the present invention. Communication end devices 102 (e.g.,computers, telephones, video conferencing units) connect through powerline 112 to one or more external networks 116. A plurality of accessunits 108 along power line 112 serve as gateways to the one or moreexternal networks 116. Access units 108 may all belong to a singleservice provider or may be employed by a plurality of different serviceproviders. Each access unit 108 may connect to a single external network116 (as shown) or to a plurality of external networks 116.

External networks 116 may include data networks, such as the Internet,switched networks, such as telephone networks and/or any othercommunication networks. In some embodiments of the invention, one ormore of external networks 116 uses electrical power lines for carryingsignals. Alternatively or additionally, external networks 116 use anyother communication medium, such as optical fibers, twin pairs and/orcable wires.

In some embodiments of the invention, power line 112 serves as amulti-device link, allowing to connect three or more devices to eachother. Generally in multi-device links, all the devices connected to themulti-device link can hear the signals transmitted by all the otherdevices. It is noted, however, that on power line 112, due to the highnoise levels, devices generally receive signals from nearby devices andnot from more remote devices.

End devices 102 optionally connect to power line 112 through respectiveuser-end modems 104. Access units 108 optionally include an access modem128, which may be a stand alone modem or may be included in a modemarray, such as a remote access server (RAS).

Power line 112 generally has changing noise and attenuation conditions.In addition, some power connections may be shut down due to maintenancehandling of the power lines. In some embodiments of the invention, someor all of user end modems 104 and access modems 128 serve additionallyas repeaters which retransmit data packets they receive back onto powerline 112, toward the destination of the data packets. Thus, a user endmodem 104 can communicate with an access modem 128 distanced from itbeyond a direct communication range. Alternatively or additionally,system 100 includes one or more repeaters 120 which do not serve as useror access modems.

As described below, each modem 104 determines, at start up and/orperiodically, an access unit 108 through which it connects to externalnetwork 116. The modem 104 optionally also determines a route to theaccess unit 108. The route may be a direct transmission route or maypass through one or more other devices, e.g., repeaters 120, modems 104and access units 108. Optionally, each modem along the route keeps trackof the next device along the route. When a packet is transmitted frommodem 104 to access unit 108, modem 104 optionally forwards the packetto the next device along the route. That next device forwards the packetto a following device along the route, until the packet reaches itsdestination. Thus, each device along the route does not necessarily havea record of the entire route.

Each access unit 108 optionally assigns to the devices it services adynamic address to be used by the device in identifying before accessunit 108. Access unit 108 optionally also assigns itself a dynamicaddress. The dynamic address of the assigning access unit 108 may have apredetermined value (e.g., 1) or may be assigned randomly or using anyother method. Optionally, each of the devices in system 100 isadditionally identified by its MAC Ethernet address which ispreconfigured in the device at the time of manufacture. The MAC Ethernetaddress optionally appears in requests for assigning a dynamic address,as described below, and/or in a payload portion of packets transmittedon power line 112. Thus, in an exemplary embodiment of the invention,two types of addresses are used to identify devices in system 100. Anexemplary method of assigning the dynamically assigned addresses to thedevices of system 100 is described hereinbelow.

FIG. 2 is a schematic illustration of a data packet transmitted on powerline 112, in accordance with an embodiment of the present invention. Thedata packet of FIG. 2 optionally includes a delimiter 152 formed of aconstant preamble 154 and a delimiter header 156. Delimiter header 156optionally states the source (SRC) 158 and destination (DST) 160 of thepacket. Optionally, the source and destination of the packet are statedusing dynamic addresses assigned to the source and destination devicesby their access unit 108. The use of the dynamically assigned addressesallows use of relatively short addresses, e.g., between 7 to 10 bits,such that the delimiter header can be kept short (e.g., 25 bits). Insome embodiments of the invention, the delimiter header further includesan identification field 162 of the access unit 108 assigning the dynamicaddresses to the source and destination. An error check field (e.g.,FCCS, CRC) 164 is optionally also included in delimiter header 156.

The identification values of access units 108 stated in field 162, areoptionally values configured by a human operator. Alternatively, when anaccess unit 108 is connected to power lines 112 it queries theneighboring devices to determine which numbers are already used forfield 162 in its vicinity. The new access unit then selects, for examplerandomly, a number not used in the vicinity.

In addition to delimiter 152, the packet of FIG. 2 optionally includes apayload 170 carrying the data of the packet. Optionally, payload 170includes a payload header 172, which includes an original source field174 and a final destination field 176. Address fields 174 and 176optionally use the dynamically assigned addresses used in delimiterheader 156. Alternatively or additionally, address fields 174 and/or 176use globally unique address values, such as the 6 byte MAC Ethernetaddresses.

Not all packets transmitted on power line 112 have the form shown inFIG. 2. For example, some control packets may include only delimiter 152and do not include a payload 170. In addition, some payloads 170 may notinclude address fields 174 and 176. For example, when a stream offragments of an original packet are transmitted together, address fields174 and 176 may be included only in one of the fragments. Furthermore,the packet of FIG. 2 is brought only by way of example, and other packetformats may be used in accordance with the present mvention.

In some embodiments of the invention, in transmitting a packet from amodem 104 to access unit 108, modem 104 generates payload 170 of thepacket including the original source and final destination addresses ofthe modem 104 and the access unit 108, respectively. In addition, modem104 prepares the delimiter header 156 of the packet, stating theidentity of access unit 108 in identification field 162, the dynamicaddress of modem 104 as source 158 and the next device along the routeto access unit 108 as destination 160. The next device along the routeoptionally leaves payload 170 unchanged, but replaces the delimiterheader 156, such that the source is the address of the next device(currently handling the packet) and the destination is the dynamicaddress of a further device along the route. The direction in which toforward the packet is optionally determined from the destination addressfield 176 in the payload 170 of the packet.

In some embodiments of the invention, each device in system 100 isregistered in a single access unit 108 and communicates only withdevices registered at the same access unit 108. Optionally, when a modem104 needs to communicate with another modem 104 assigned to a differentaccess unit 108, the communication is performed using a differentprotocol than used for communicating with access unit 108, for exampleas described in PCT application PCT/IL02/00582, titled “Dual PurposePower Line Modem”, filed Jul. 17, 2002, the disclosure of which isincorporated herein by reference. Alternatively or additionally, anycommunication between peer modems 104 uses a different protocol thanused for communicating with access unit 108, regardless of the accessunits 108 at which the peer moderns are registered. Furtheralternatively or additionally, different protocols may be used incommunicating with different access units 108.

Alternatively or additionally, some of the devices of system 100 (e.g.,modems 104, repeaters 120 and/or access units 108) have a plurality ofdynamic addresses registered at different access units 108, and thesedevices are used as bridges in communicating between modems 104registered in different access units 108. In an exemplary embodiment ofthe invention, each repeater 120 registers with all access units 108that are within a predetermined number of hops from the repeater.Optionally, for each access unit 108, repeaters 120 manage a routingtable which identifies the dynamic address of the next device to be usedfor each modem 104 having a route through the repeater to access unit108 and/or the next device for each access unit 108. Thus, repeaters 120can be used to lead packets to different access units 108. Thispossibility is especially useful when neighboring modems 104 need toreceive service from different access units 108, for example accessunits belonging to different service providers and/or leading todifferent external networks.

In some embodiments of the invention, each user-end modem 104 manages amapping table, which is used in selecting an access unit 108 to servicethe modem, for example using the method described below. Optionally, themapping table includes an entry for each neighboring device of themodem, i.e., for each device which is in direct transmission range fromthe modem (including devices not registered to the same access unit108). In each entry, the table optionally lists an access unit 108 towhich the neighboring device is assigned and/or an access unit having alowest cost path from the device. In addition, each entry optionallyincludes data on the route to the access unit and/or data on the accessunit. The data on the route optionally includes the neighboring deviceleading to the access unit and/or a cost of the route. The data on theaccess unit optionally includes the service provider maintaining theaccess unit, the external network (or networks) to which the access unitconnects and/or the price charged by the service provider of the accessunit.

In some embodiments of the invention, each entry of the mapping tableincludes a master field, which defines a device through which the routeto access unit 108 must pass. The use of the master field may beoptional or mandatory. The master device may be an access unit 108 towhich the modem 104 must connect and/or an intermediate device throughwhich the connection must pass. The master device may be defined, forexample, when too many fluctuations in the routing path are not desiredand/or when the master device is required for a specific task, forexample for monitoring the data of the end user. Alternatively oradditionally, the master device defines a specific access unit whichmust be used, for example when only that access unit leads to a desiredexternal network 116.

Each entry of the mapping table optionally includes a time stamp fieldidentifying the last time in which the route was verified with theneighboring device and/or the most recent time at which thecommunication with the neighboring device was verified. Optionally,entries older than a predetermined amount of time, for example 10minutes, are removed from the table. In some embodiments of theinvention, before removing an entry from the table, modem 104 attemptsto communicate with the neighboring device of the entry. When an entryrelating to the access unit 108, currently servicing the modem, isremoved from the table, a different access unit 108 is selected. Modem104 optionally transmits a provisioning request to the newly selectedaccess unit 108, as described below with reference to FIG. 3.

Alternatively to the mapping table having an entry for each neighboringdevice, the mapping table has an entry for each access unit 108. Foreach access unit 108, the table optionally lists the best (e.g., lowestcost) neighboring device through which to access the access unit 108.Further alternatively, the mapping table has an entry for each pair ofaccess unit 108 and neighboring device, such that backup data is alwaysavailable in case of changes in the network map (e.g., failure of adevice) and there is no need to wait for a new network discoveryprocedure.

FIG. 3 is a flowchart of acts performed by a user-end modem 104 and itsneighboring devices, in selecting an access unit 108 from which toreceive service, in accordance with an embodiment of the presentinvention. Optionally, modem 104 transmits (200) one or more broadcastnetwork discovery packets on power lines 112. The neighboring devices(e.g., other user-end modems 104, repeaters 120, access modems 128)receiving the network discovery packet respond (202) on power lines 112with a response including information they include in their mappingtable. In some embodiments of the invention, modem 104 determines (204)the cost of communicating with each of the responding devices. Accordingto the determined cost and the received responses, the mapping table ofmodem 104 is updated (206).

Based on the updated mapping table, an access unit 108 to service modem104 is optionally selected (208). The selection is optionally performedsolely based on the cost. Alternatively, the selection is based on otherinformation, such as the QoS policy of access unit 108 and/or the loadon the access unit.

In some embodiments of the invention, modem 104 transmits (210) to theselected access unit 108 a provisioning request, which requests theaccess modem 108 to provide access service to the modem 104. Theprovisioning request is optionally transmitted to access unit 108 alongthe determined route, as described above regarding data packets.

The selected access unit 108 optionally responds (212) to theprovisioning request with a provisioning authorization message. Theprovisioning authorization message optionally includes the dynamicaddress assigned to the requesting modem 104. The intermediate devicesalong the route from access unit 108 to requesting modem 104, if suchintermediate devices exist, optionally register the identity of therequesting modem 104 and the neighboring device to which packetsdirected to that modem are to be forwarded. The registered identity andneighboring device used to route to it, referred to herein as routingdata, are optionally used in forwarding data packets from access unit108 to modem 104.

In some embodiments of the invention, the provisioning authorizationmessage includes information on the VLANs supported by access unit 108,the QoS of the access unit, its IP configuration and/or other unitparameters. This information may be general for all modems handled byaccess unit 108 and/or may include specific parameters for the specificmodem 104.

Modem 104 optionally acknowledges (214) the receipt of the provisioningauthorization message.

The method of FIG. 3 is optionally performed each time modem 104 isoperated and/or when the access unit 108 currently servicing modem 104does not respond for over a predetermined amount of time. Alternativelyor additionally, the method of FIG. 3 is performed periodically, forexample every 5-10 minutes. In some embodiments of the invention, eachtime the method of FIG. 3 is performed, a provisioning request istransmitted (210) to a selected access unit 108. Alternatively, aprovisioning request is transmitted only when the selected access unit108 is different from the access unit currently used by the modem 104,if there is such an access unit 108.

In some embodiments of the invention, an access unit 108 which isdifferent from the currently used access unit is selected only if thecost of the selected access unit is substantially lower than thecurrently used access unit, for example by 25-40%. Thus, resources arenot spent on changing the access unit 108 used, for a small gain.Alternatively, a change in the access unit 108 used, is performed evenwhen a marginal gain in cost is involved, so as to continuously providebest communication service possible.

Referring in more detail to transmitting (200) the one or more networkdiscovery packets, in some embodiments of the invention, a sequence oftwo to four discovery packets are transmitted, in order to reduce thechances of packet loss. Alternatively or additionally, if fewer than apredetermined number of responses are received, modem 104 repeats thetransmission of the network discovery packet (or packets). In someembodiments of the invention, the predetermined number of requiredresponses which causes modem 104 to stop retransmitting is one.Alternatively, at least two, three or more responses are required, so asto allow for redundancy and/or better selection of an access unit 108.The more data available to modem 104, the better the selection of alowest cost path to an access unit 108. In some embodiments of theinvention, repeating the transmission is performed in predeterminedinterval periods, e.g., every 24 seconds. Alternatively or additionally,repeating the transmissions is performed in increasing durations and/orusing any repetition scheme known in the art. Optionally, therepetitions are stopped after a predetermined time, for example, after60 seconds, at which time it is assumed that all the neighboring unitshave responded (e.g., there are no available neighboring devices).

In some embodiments of the invention, the network discovery packet mayindicate a specific service provider which must be used by modem 104.Optionally, in such cases, all responses include only informationrelating to the specific service provider. In some embodiments of theinvention, only devices assigned to an access unit 108 belonging to thespecified service provider respond. Alternatively, devices assigned toan access unit 108 not belonging to the specified service provider,respond with information on an access unit 108 belonging to thespecified service provider, although the device is not assigned to thataccess unit. Optionally, in this alternative, if modem 104 chooses toform a route to an access unit through the responding neighboringdevice, the neighboring device serves as a repeater for the packets ofmodem 104, although the neighboring device is not assigned to the sameaccess unit as modem 104. Alternatively or additionally, if possible,the neighboring device registers with the access unit selected by modem104 instead of the access unit 108 to which it was registered.

Further alternatively, all devices respond, such that the modem 104 isnotified of the existence of the neighboring devices. Alternatively oradditionally, the broadcast message may indicate a specific access unit108 which is to be used and/or a specific master device which must beused.

In some embodiments of the invention, the network discovery message istransmitted at the lowest transmission rate and/or in a robusttransmission format used in system 100, such that the chances ofreceiving responses is maximized.

In some embodiments of the invention, instead of transmitting thenetwork discovery packet, each device connected to power line 112periodically transmits network description packets including theinformation in their mapping table. A modem 104 connecting to thenetwork listens for these packets and accordingly selects an access unit108. Optionally, if after a predetermined amount of time modem 104 didnot receive any network description packets, the modem transmits anetwork discovery packet, to which the neighboring devices are toimmediately respond.

Referring in more detail to the devices responding (202) to the networkdiscovery packets, in some embodiments of the invention, each responsepacket identifies a single best access unit 108 and provides data onlyfor that unit. Alternatively, each response packet includes the entiremapping table of the responding device. The response optionally alsocomprises information identifying the responding device, for example theEthernet MAC address of the device and/or a dynamically provided addressof the device in system 100.

For each access unit 108 identified by the response, the responseoptionally includes an address of the access unit 108, a cost ofaccessing the access unit from the responding device, a provider name ofthe access unit and a time stamp of the provided data. Alternatively oradditionally, the data for each access unit 108 includes a set ofvirtual local area networks (VLANs) the access unit supports, a qualityof service (QoS) policy of the access unit and/or a current loadindication of the access unit. In some embodiments of the invention, theaddress of the access unit 108 comprises an Ethernet MAC address.Alternatively or additionally, the address of the access unit 108comprises an address dynamically selected by the access unit, withinsystem 100.

Referring in more detail to determining (204) the cost of communicatingwith each of the responding devices, in some embodiments of theinvention, the cost is determined from the responses. Optionally, theresponse packet is analyzed to determine the channel quality from theresponding device to modem 104. In some embodiments of the invention,the response includes a special sequence content which is used fordetermining the channel quality. Alternatively or additionally, thefields of the packet used for transferring the response are also used indetermining the channel quality. In some embodiments of the invention,the responses include a time stamp from which the delay of the packet isdetermined. Optionally, modem 104 compares the time stamp of the packetto the current time and accordingly determines the round trip delay(RTD) to the neighboring unit. The RTD is optionally used in calculatingthe cost of the route to the neighboring device.

Alternatively or additionally, modem 104 transmits to some or all of theresponding devices, channel quality estimation packets, separate fromthe network query packets and their responses. The responses to thechannel quality estimation packets are optionally used in determining(204) the cost of communicating with the responding device.

Referring in more detail to updating (206) the mapping table, in someembodiments of the invention, the cost of each access unit 108 isdetermined as the sum of the cost received from the responding device(i.e., the cost of the path from the access unit 108 to the neighboringdevice) together with the cost of communicating with the respondingdevice. Optionally, each table entry indicates the number of hopsrequired to reach the access unit 108. The number of hops is optionallydetermined as the number of hops received from the responding deviceplus 1, for the hop from the neighboring device to modem 104. In someembodiments of the invention, access units 108 requiring more than apredetermined number of hops are not taken into consideration.Alternatively or additionally, the number of hops required to reach eachaccess unit is taken into account in determining the cost of the path tothe access unit.

In some embodiments of the invention, the cost of the route between amodem 104 and an access unit 108 is a function of the number ofintermediate devices along the route and the bit rate of the hops (i.e.,the segments connecting two devices along the route) of the route. Thecost of the route is optionally a function, only or mainly (regardingthe bit rate portion of the function), of the lowest bit rate along theroute, as this lowest bit rate is a bottleneck of the route.Alternatively or additionally, the cost of the route is a function ofthe average bit rate of the route, since the higher bit rate hops reducethe number of packets required and thus reduce the chances of collisionson power line 112, even if the bottleneck prevents achieving fastertransmission. Alternatively or additionally, the cost of the route isdetermined based on round trip delay measurements, as described above.

In an exemplary embodiment of the present invention, the cost is definedby:${\cos\quad t} = {k \cdot {\sum\limits_{i}^{\quad}\quad\frac{1}{{bit}\quad{rate}\quad{of}\quad{hop}\quad i}}}$where i runs over all the hops between modem 104 and access unit 108 andk is a constant.

In some embodiments of the invention, the network discovery packets aretransmitted without a dynamic address of modem 104, as in some cases(e.g., a newly connected modem) such an address was not yet assigned.Alternatively or additionally, when the network discovery packets aretransmitted for update purposes by a modem 104 already having a dynamicaddress, the dynamic address is included in the network discoverypackets. Optionally, the network discovery packets include in theirpayload the Ethernet MAC address of modem 104 for identification ofmodem 104. The response packets are optionally transmitted as broadcastpackets carrying the source dynamic address of the responding device.Optionally, only modems 104 that recently transmitted network discoverypackets examine these response packets to determine if they are directedto them.

The provisioning request is optionally transmitted to the neighboringdevice leading to the selected access unit 108 without a dynamic sourceaddress, but with a source Ethernet MAC address in the payload. Theprovisioning authorization message including the dynamic address of themodem 104 is optionally transmitted from the neighboring device to themodem 104 as a broadcast message. Thereafter, the modem 104 can use itsdynamic address for all further communications.

In some embodiments of the invention, user-end modems 104 may adjusttheir transmission power level, so as to control the range of deviceswhich receive the packets transmitted by the modem 104 and hence therange of devices to which transmissions of modem 104 interfere. The datarate of the transmission between two devices optionally depends on thepower level used for the transmission. Thus, in some cases, the datarate may be increased by increasing the transmission power. The controlof the transmission power level is optionally performed as described inthe above mentioned PCT publication WO 02/15413.

In some embodiments of the invention, the mapping table includes foreach entry, an indication of the transmission power level required forreaching the neighboring device of the entry. Optionally, in theseembodiments, transmitting (200) the one or more network discoverypackets comprises transmitting packets at a plurality of different powerlevels. The power level required for communicating with each neighboringdevice is optionally determined as the lowest power level to which theneighboring device responded. In some embodiments of the invention, themethod of FIG. 3 is started with transmitting network discovery packetswith a low transmission power. If a sufficient number of responses,optionally with sufficiently high data rates, are not received, thetransmission of network discovery packets is repeated with a highertransmission power. This process is optionally repeated until asufficient number of responses is received and/or a predetermined powerlevel is reached. Alternatively, a plurality of network discoverypackets are transmitted at a predetermined set of power levels, and thenumber of power levels used does not depend on the received responses.

Each entry of the mapping table optionally lists a best pair of powerlevel and data rate determined for the connection between modem 104 andthe neighboring device. Alternatively, each entry lists a plurality ofpairs of power levels and data rates.

In some embodiments of the invention, the selecting (208) of the accessunit 108 depends on the power level used to contact the neighboringdevice leading to the selected access unit 108. Optionally, aneighboring device and access unit 108 having a best cost with a lowesttransmission power level are selected, provided the cost of the path islower than a predetermined threshold value. If the best cost is notlower than the threshold, a higher power level is optionally used.Alternatively, a higher transmission power level is used when the ratiobetween the cost reduction and the power increase is greater than apredetermined value. Further alternatively or additionally, the cost isa function of the power level. In an exemplary embodiment of theinvention, the cost increases with the number of devices that neighbormodem 104 for the power level used. The more neighboring devices thereare, the larger the area which cannot transmit packets concurrently withmodem 104. The number of neighboring devices is optionally determinedaccording to the number of devices responding to the network discoverypackets transmitted at the power level.

It will be appreciated that the above described methods may be varied inmany ways, including, changing the order of acts, and/or performing aplurality of acts concurrently. It should also be appreciated that theabove described description of methods and apparatus are to beinterpreted as including apparatus for carrying out the methods andmethods of using the apparatus.

The present invention has been described using non-limiting detaileddescriptions of embodiments thereof that are provided by way of exampleand are not intended to limit the scope of the invention. For example,the method of FIG. 3 may be used by repeaters 120 and/or access units108 (e.g., when their connection to external network 116 is notoperable), in registering to an access unit 108. It should be understoodthat features and/or acts described with respect to one embodiment maybe used with other embodiments and that not all embodiments of theinvention have all of the features and/or steps shown in a particularfigure or described with respect to one of the embodiments. Variationsof embodiments described will occur to persons of the art.

It is noted that some of the above described embodiments may describethe best mode contemplated by the inventors and therefore may includestructure, acts or details of structures and acts that may not beessential to the invention and which are described as examples.Structure and acts described herein are replaceable by equivalents whichperform the same function, even if the structure or acts are different,as known in the art. Therefore, the scope of the invention is limitedonly by the limitations used in the claims. When used in the followingclaims, the terms “comprise”, “include”, “have” and their conjugatesmean “including but not limited to”.

1. A method of connecting a power line modem to an external network,comprising: receiving, by the power line modem, a plurality of packetsdirectly transmitted from a plurality of neighboring devices connectedto the power lines; and selecting, by the power line modem, an accessunit to service the power line modem, responsive to the received packetsfrom the plurality of neighboring devices.
 2. A method according toclaim 1, wherein at least one of the neighboring devices comprises anaccess unit.
 3. A method according to claim 1 or claim 2, wherein atleast one of the neighboring devices is not an access unit.
 4. A methodaccording to claim 3, wherein at least one of the neighboring devicescomprises a second user modem.
 5. A method according to claim 1,comprising determining for each of the plurality of neighboring devices,a cost of a route to an access unit, through the neighboring device,responsive to the received packets and wherein selecting the access unitis performed responsive to the determination of the costs.
 6. A methodaccording to claim 5, wherein determining for the plurality ofneighboring devices the cost of a route to an access unit comprisesdetermining for a plurality of the neighboring devices the cost ofroutes to a single access unit.
 7. A method according to claim 5,wherein determining for the plurality of neighboring devices the cost ofa route to an access unit comprises determining for a plurality of theneighboring devices the cost of routes to a plurality of differentaccess units.
 8. A method according to claim 7, wherein selecting theaccess unit comprises selecting responsive to the determined cost andresponsive to one or more parameters of the different access units.
 9. Amethod according to claim 8, wherein selecting the access unit comprisesselecting responsive to the determined cost and responsive to the loadon the different access units.
 10. A method according to claim 8,wherein selecting the access unit comprises selecting responsive to thedetermined cost and responsive to the external networks to which thedifferent access units lead.
 11. A method according to claim 5, whereindetermining the cost comprises determining the cost responsive to anumber of intermediate devices along the route to the access unit.
 12. Amethod according to claim 5, wherein determining the cost comprisesdetermining the cost responsive to a data rate of one or more hops ofthe route to the access unit.
 13. A method according to claim 5, whereindetermining the cost comprises determining the cost responsive to apower level required to communicate with the neighboring device.
 14. Amethod according to claim 13, wherein determining the cost comprisesdetermining the cost responsive to a number of neighboring devices ofthe modem at the required power level.
 15. A method according to claim5, wherein determining the cost comprises determining a neighbor segmentcost of a network segment between the power line modem and a neighboringdevice and adding the neighbor segment cost to an access cost of asegment from the neighboring device to an access unit, which access costis received from the neighboring device.
 16. A method according to claim1, wherein the received plurality of packets are generated by theneighboring devices, periodically, without receiving prompting messagesfrom the power line modem.
 17. A method according to claim 1, comprisingtransmitting one or more network discovery packets on the power line andwherein the received plurality of packets are generated responsive to atleast one of the one or more discovery packets.
 18. A method accordingto claim 17, wherein transmitting the one or more network discoverypackets comprises transmitting a plurality of packets with differenttransmission power levels.
 19. A method according to claim 18,comprising determining for each of the power levels a number of devicesresponding to the transmitted packet with that power level.
 20. A methodaccording to claim 17, wherein transmitting the one or more networkdiscovery packets comprises transmitting with increasing power levelsuntil a route with a cost beneath a predetermined threshold is found.21. A method according to claim 1, wherein the selected access unit isnot within a transmission range of the power line modem.
 22. A powerline modem, comprising: a power line interface for receiving packetsfrom the power line; and a controller adapted to receive a plurality ofpackets directly transmitted from a plurality of neighboring devicesconnected to the power lines and to select an access unit from which toreceive service, responsive to the received packets from the pluralityof neighboring devices.
 23. A power line modem according to claim 22,wherein the controller is adapted to determine, for the plurality ofneighboring devices, a cost of a route to an access unit, through theneighboring device, responsive to the received packets and the selectionof the access unit is performed responsive to the determination of thecosts.